Genetic code and its relationship to cellular function

The genetic code & codon table (article) | Khan Academy

genetic code and its relationship to cellular function

In this article, we'll take a closer look at the genetic code, which allows DNA and . Because the code is essential to the function of cells, it would tend to remain. These RNA structure-mediated functions also include regulation of nearly every step of cellular protein production. Some of the regulatory. Everything in our cells is ultimately built based on the genetic code. Structures made of RNA perform important functions in ourselves, including assembling.

From DNA to protein - 3D

Making a protein Genes that provide instructions for proteins are expressed in a two-step process. In translation, the sequence of nucleotides in the mRNA is "translated" into a sequence of amino acids in a polypeptide protein chain.

If this is a new concept for you, you may want to learn more by watching Sal's video on transcription and translation. Codons Cells decode mRNAs by reading their nucleotides in groups of three, called codons. Here are some features of codons: Most codons specify an amino acid Three "stop" codons mark the end of a protein One "start" codon, AUG, marks the beginning of a protein and also encodes the amino acid methionine Codons in an mRNA are read during translation, beginning with a start codon and continuing until a stop codon is reached.

The genetic code table The full set of relationships between codons and amino acids or stop signals is called the genetic code. The genetic code is often summarized in a table. Notice that many amino acids are represented in the table by more than one codon. For instance, there are six different ways to "write" leucine in the language of mRNA see if you can find all six.

genetic code and its relationship to cellular function

An important point about the genetic code is that it's universal. That is, with minor exceptions, virtually all species from bacteria to you!

genetic code and its relationship to cellular function

Reading frame To reliably get from an mRNA to a protein, we need one more concept: Reading frame determines how the mRNA sequence is divided up into codons during translation. That's a pretty abstract concept, so let's look at an example to understand it better. The mRNA below can encode three totally different proteins, depending on the frame in which it's read: So, how does a cell know which of these protein to make?

AUG is the codon for methionine, and is also the start codon. Thus, every polypeptide typically starts with methionine, although the initial methionine may be snipped off in later processing steps.

genetic code and its relationship to cellular function

A start codon is required to begin translation, but the codon AUG can also appear later in the coding sequence of an an mRNA, where it simply specifies the amino acid methionine. Once translation has begun at the start codon, the following codons of the mRNA will be read one by one, in the 5' to 3' direction. As each codon is read, the matching amino acid is added to the C-terminus of the polypeptide.

Most of the codons in the genetic code specify amino acids and are read during this phase of translation. How do you read the codon table?

The codon table may look kind of intimidating at first. Fortunately, it's organized in a logical way, and it's not too hard to use once you understand this organization. To see how the codon table works, let's walk through an example. Suppose that we are interested in the codon CAG and want to know which amino acid it specifies.

The genetic code (article) | Khan Academy

First, we look at the left side of the table. The axis on the left side refers to the first letter of the codon, so we find C along the left axis. This tells us the broad row of the table in which our codon will be found.

Next, we look at the top of the table. The upper axis refers to the second letter of the codon, so we find A along the upper axis. This tells us the column of the table in which our codon will be found.

There was a problem providing the content you requested

The row and column from steps 1 and 2 intersect in a single box in the codon table, one containing four codons. It's often easiest to simply look at these four codons and see which one is the one you're looking for. If you want to use the structure of the table to the maximum, however, you can use the third axis on the right side of the table corresponding to the intersect box.

By finding the third nucleotide of the codon on this axis, you can identify the exact row within the box where your codon is found. For instance, if we look for G on this axis in our example above, we find that CAG encodes the amino acid glutamine Gln. Translation continues until a stop codon is reached. Unlike start codons, stop codons don't correspond to an amino acid. Instead, they act as "stop" signals, indicating that the polypeptide is complete and causing it to be released from the ribosome.

genetic code and its relationship to cellular function

More nucleotides may appear after the stop codon in the mRNA, but will not be translated as part of the polypeptide. Reading frame The start codon is critical because it determines where translation will begin on the mRNA. Most importantly, the position of the start codon determines the reading frame, or how the mRNA sequence is divided up into groups of three nucleotides inside the ribosome.